1. Field of the Invention
The present invention relates to a technique for detecting ink within a tank for containing the ink.
2. Description of the Related Art
Image recording apparatus include a copier, a printer, a facsimile, etc. In the copier, a reading mechanism, such as an image reading apparatus, etc., for reading a manuscript is provided, and image recording is made by imaging and fusing the manuscript read by the reading mechanism on printing paper. The printer makes image recording by imaging and fusing pictorial data transmitted from a computer, etc. on printing paper. Additionally, the facsimile makes image recording by imaging and fusing pictorial data transmitted via a telephone line, etc. on printing paper.
A printer, which comprises an inkjet head, forms and records a graphic, a character, etc. on a recording medium by spraying ink droplets onto paper or other recording medium, has been attracting attention in recent years. Since this printer normally uses a replaceable ink tank of a sealed type, an ink remaining amount detecting sensor must be provided to detect and display the remaining amount of ink within the ink tank.
As a conventional ink remaining amount detecting sensor, for example, a sensor disclosed by Japanese Published Examined Patent Application No. H3-55313 is known. In this sensor, two electrodes made of stainless steel, which are arranged to be soaked in ink within an ink tank, are provided, and the resistance value of the ink between the electrodes is monitored by applying a voltage in between the electrodes, thereby detecting the remaining amount of the ink within the tank.
Additionally, for example, also Japanese Published Unexamined Patent Application No. H10-175312 discloses a technique for measuring the remaining amount of ink. An ink remaining amount detecting device according to this technique comprises a detecting unit, a measuring unit, and a controlling unit. Here, the detecting unit detects an ultrasound wave, which is propagated with a transmission/reception element arranged on the bottom of an ink tank or with a transmission/reception element arranged vertically lower than a surface on which an ink supply hole exists, is reflected on the surface of an ink liquid and comes back to the transmission/reception element. The measuring unit measures, via the controlling unit, a time required from when the ultrasound wave is transmitted from the transmission/reception element until when the ultrasound wave is reflected on the surface of the ink liquid and comes back to the transmission/reception element. The controlling unit detects the value of the liquid surface level of the ink within the ink tank from the required time measured by the measuring unit. This device measures the remaining amount of ink in this way.
However, with the technique, which is disclosed by the above described Japanese Published Examined Patent Application No. H3-55313, for causing ink to contact electrodes in order to detect the remaining amount of the ink, an electric current is made to flow into the ink via the electrodes, and accordingly, the components of the ink is electrolyzed, and the quality of the ink alters.
Additionally, the device disclosed by the above described Japanese Published Unexamined Patent Application No. H10-175312 has a problem that the phenomenon of a near sound field is not considered. This problem is described.
FIG. 1 shows the state of propagation of an ultrasound wave generated by a piezoelectric element. This figure shows the state where the ultrasound wave propagates from the piezoelectric element 111 accommodated within an ultrasound wave transmission mechanism 112 to a medium 113. Here, a white portion within the medium 113 indicates a portion where a sound pressure is high, whereas a black portion indicates a portion where the sound pressure is low.
As shown in this figure, in a far sound field 115, which is a portion far from the piezoelectric element 111 within the medium 113, the pattern of the white portion is stable, and exhibits acute linearity. In the meantime, in a near sound field 114 in the neighborhood of the piezoelectric element 111, the white portion has a fine pattern, which indicates a complicated change in the sound pressure. The near sound field 114 is generated by interference between ultrasound waves emitted from the central portion of the piezoelectric element 111 and from its end among ultrasound waves emitted from the piezoelectric element 111. This phenomenon is also called a near interference zone (Fresnel zone), etc.
With the technique disclosed by the above described Japanese Published Unexamined Patent Application No. H10-175312, the characteristic of an ultrasound wave in such a near sound field is not considered. Therefore, a wave reflected on the surface of an ink liquid cannot be identified due to the influence of the characteristic, and the remaining amount of ink cannot be properly obtained in some cases.